1. Field of the Invention
The present invention relates to a storage battery managing apparatus for managing charge-discharge of a storage battery and a vehicle controlling apparatus providing the same. More particularly, the present invention relates to a storage battery managing apparatus suitable for charge-discharge control of a battery pack composed of a plurality of unit cells, and a vehicle controlling apparatus providing the same.
2. Description of the Related Art
A vehicle is provided with a storage battery, such as a lead-acid battery, a nickel hydride battery, a lithium ion battery, or the like mounted thereon. The power necessary to start up an engine, use electric equipment, or drive a hybrid car or an electric vehicle is supplied from the storage battery.
The storage battery is provided with a maximum permissible current that can be inputted or outputted according to the present state. If the storage battery is charged or discharged with the maximum permissible current exceeded, the battery voltage deviates from a normal control range possibly resulting in overcharge or overdischarge. Generally, the higher the SOC (State Of Charge) of the storage battery, the smaller a maximum permissible charge current and the larger a maximum permissible discharge current. Further, the lower the SOC of the storage battery, the smaller the maximum permissible discharge current and the larger the maximum permissible charge current. In order to optimally use the storage battery, it is necessary to control the charge and discharge of the storage battery within a range of the maximum permissible current according to various states of the storage battery.
Generally, a battery pack having a plurality of unit cells is used as a storage battery for hybrid cars and electric vehicles. If state variations occur in the plurality of unit cells included in the battery pack, the maximum permissible current differ for each unit cell. Therefore, it is necessary to control the charge and discharge of the storage battery in consideration of state variations is required.
Conventionally, as a technique for a charge-discharge controlling apparatus for a chargeable-dischargeable battery pack composed of a plurality of cells, a technique disclosed, for example, in JP-A-2005-117722 is known. With the technique, the SOC of each cell is detected and the upper-limit value used as a target value for stopping the charge of the battery pack-and the lower-limit value used as a target value for stopping discharge thereof are changed based on the SOC of each cell.